1. Field of the Invention
This invention relates to a multiple element fuse and in particular a multiple element fuse of open construction wherein each fusible element is mounted within an insulative tube.
2. Description of the Prior Art
Prior art multiple element fuses often include a plurality of fusible elements each mounted within an insulative tube. Fusible elements mounted in this fashion are commonly referred to as "tube fuses". Such multiple element fuses conventionally have end bells soldered at opposite ends to the tube fuses, the tube fuses being exposed therebetween. Devices of this type are designed to operate near their current carrying capacity and require an open construction to allow greater air cooling of the individual tube fuses. It is frequently desirable to provide air flow through the interior of the fuse, or to otherwise provide a forced cooling of the tube fuses.
A blade terminal typically is formed with or joined to the end bells of the multiple element fuses for connection with bolts or similar fasteners to elongated busbars of electrical equipment. Frequently, the busbars are not spaced apart to the exact distance required or have mounting holes otherwise misaligned with the mounting holes located in the blade terminals of the multiple element fuses. As such, one or both of the busbars must be deflected to provide alignment with the blade terminals, to allow a bolted connection to be made therebetween. This frequently imposes tensile and cantilever forces on the multiple element fuse end bells. As such, when the fuse operates to clear an electrical overload, the soldered connection between the end bells and the tube fuses sometimes softens or melts sufficiently to allow the busbars to resume their rest position, thus pulling the fuse apart, causing the individual tube fuses to fall away, possibly into the switch gear within which the fuse is installed.
In order to avoid the damage potential of fuse parts falling into the switch gear, fuses could be constructed with fusible elements which stay relatively cool during normal and clearing operations. However, this severely limits the ability of the tube fuses to operate near their current carrying capacity and thus greatly increases clearing I.sup.2 t.